Self‐emulsification synthesis of epoxy phosphate ester and its flame‐retardant mechanism in flexible poly(vinyl chloride)/magnesium hydroxide composites

Abstract A trade‐off dilemma exists for simultaneously improving the mechanical properties and flame resistance of flexible polyvinyl chloride (fPVC)/magnesium hydroxide (MH) composites. In this study, epoxy phosphate ester (EPE), a hydrophobic surface modifier of MH, was synthesized using a self‐emulsification method. After modification, EPE was bonded to the surface of MH (MHEPE) without altering its morphology. The results of limiting oxygen index and cone calorimetry tests indicated that fPVC/MHEPE exhibited better flame retardancy and smoke suppression effects than did fPVC/MH. The peak of the heat release rate, total heat release, peak of the smoke production rate, and total smoke production of the fPVC/MHEPE composite were 206.0 kJ m −2 , 45.90 MJ m −2 , 0.0729 m 2 s −1 , and 9.88 m 2 , which were 8.64%, 14.00%, 27.61%, and 9.02% lower than those of the fPVC/MH composite, respectively. For the fPVC/MHEPE composite, a compact and continuous char residue formed, which could inhibit heat and flammable volatile migration between the matrix and burning zones. In the gas phase, the dilution effect of H 2 O vapor reduced the concentrations of O 2 and flammable volatiles. The free‐radical quenching effect of ·PO and ·PO 2 also played a vital role in extinguishing flame and terminating combustion. Further, the introduction of EPE improved the tensile and impact strengths of the fPVC/MH composites because of the excellent interfacial compatibility between MHEPE and the fPVC matrix. This study provides a simple and workable solution for the trade‐off dilemma, and the remarkable flame retardancy and mechanical properties of the fPVC/MHEPE composite render it a promising cable material.